This application is an application under 35 U.S.C. Section 371 of International Application Number PCT/FR99/02483 filed on Oct. 13, 1999.
The present invention relates to the use as filler, in rubber compositions, of amorphous aluminum hydroxycarbonate, hydroxyoxycarbonate or oxycarbonate.
It also relates to the rubber compositions thus obtained.
Finally, it also relates to finished articles based on these compositions and in particular to tire covers.
It is known to employ reinforcing white fillers in elastomers, such as, for example, precipitated silica or alumina. However, the results are not always those hoped for.
The aim of the invention is to provide a filler for rubber compositions which provides them with a satisfactory compromise with regard to properties, namely, preferably:
very good rheological properties and excellent suitability for vulcanization, comparable with those of highly dispersible precipitated silicas but much better than those provided by alumina,
particularly outstanding dynamic properties, in particular a Payne effect of low amplitude, resulting in a low resistance to rolling for tires based on these compositions, and/or a very high tangent xcex4 at 0xc2x0 C., resulting in an improved adhesion for tires based on these compositions,
good strengthening in terms of modulus,
a rather high resistance to thermal aging and to UV (ultraviolet radiation) aging.
With this aim, a subject matter of the present invention is the use as filler, in a rubber composition, of at least one compound (A) composed of an amorphous aluminum hydroxycarbonate or an amorphous aluminum hydroxyoxycarbonate or an amorphous aluminum oxycarbonate.
More particularly, said hydroxycarbonate, hydroxyoxycarbonate or oxycarbonate comprises at least 0.01, in particular at least 0.04, mol of carbonate per mole of aluminum; it can comprise at least 0.1 mol of carbonate per mole of aluminum. In general, its carbonate/aluminum molar ratio is at most 0.25, in particular at most 0.2.
The carbonates present in the hydroxycarbonate, hydroxyoxycarbonate or oxycarbonate and which can be detected by infrared spectroscopy are usually covalent.
The compound (A) generally has a BET specific surface area of between 40 and 150 m2/g, in particular between 45 and 95 m2/g; it can be between 50 and 75 m2/g. The BET surface area is determined according to the Brunauer-Emmet-Teller method described in xe2x80x9cThe Journal of the American Chemical Societyxe2x80x9d, Vol. 60, page 309, February 1938, which corresponds to NF Standard T 45007 (November 1987).
This compound (A) preferably exhibits a low proportion of reactive surface Alxe2x80x94OH functional groups.
Some preferred but nonlimiting alternative forms of the invention are described below.
According to a first alternative form of the invention, the compound (A) employed is an amorphous aluminum hydroxycarbonate corresponding to the following empirical formula (I)
Al(OH)x(CO3)y.zH2Oxe2x80x83xe2x80x83(I)
in which
0.5xe2x89xa6xxe2x89xa63, for example 1xe2x89xa6xxe2x89xa63
0.01xe2x89xa6yxe2x89xa60.25, for example 0.04xe2x89xa6yxe2x89xa60.25, in particular 0.1xe2x89xa6yxe2x89xa60.25
zxe2x89xa61.5, for example zxe2x89xa61
In this formula (I), y can be at most equal to 0.2.
In the context in particular of this alternative form of the invention, the compound (A) preferably has the following property: it remains amorphous (its X-ray diffraction spectrum remains flat) after having been calcined (under air) for 2 hours at any temperature between 150 and 700xc2x0 C. or after having been subjected to a treatment which consists of a rapid dehydration using a gas stream at 600xc2x0 C., the contact time of the compound with this gas being from 1 to 2 seconds.
In this alternative form of the invention, the compound (A) is generally formed of aggregates of individual particles which are not or not very porous, for example substantially spherical, with a size which can be between 15 and 25 nm.
According to a second alternative form of the invention, the compound (A) employed results from the calcination (in particular under air) at any temperature between 150 and 700xc2x0 C., in particular between 180 and 650xc2x0 C., of an amorphous aluminum hydroxycarbonate (known as starting amorphous aluminum hydroxycarbonate), in particular for 1 to 3 hours, for example for 2 hours.
In this alternative form, the starting amorphous aluminum hydroxycarbonate preferably has the following property: it remains amorphous after having been subjected to a treatment which consists of a rapid dehydration using a gas stream at 600xc2x0 C., the contact time of the compound with this gas being from 1 to 2 seconds.
According to a third alternative form of the invention, the compound (A) employed results from the rapid dehydration of an amorphous aluminum hydroxycarbonate (known as starting amorphous aluminum hydroxycarbonate) using a gas stream at a temperature of between 500 and 700xc2x0 C., in particular equal to 600xc2x0 C., the contact time of this starting amorphous aluminum hydroxycarbonate with this gas being between a fraction of a second and 4 seconds, in particular between 1 and 2 seconds.
In this alternative form, the starting amorphous aluminum hydroxycarbonate preferably has the following property: it remains amorphous after having been calcined (under air) for 2 hours at any temperature between 150 and 700xc2x0 C.
In the second and third alternative forms in particular of the invention, the compound (A) employed advantageously exhibits a high dispersibility. This dispersibility is quantified using the measurement of the level of fines (xcfx84f), that is to say of the proportion (by weight) of particles with a size of less than 0.3 xcexcm, after deagglomeration with ultrasound, carried out according to the test described below.
In this test, the ability of the compound to disperse is measured by a particle size measurement (by sedimentation) carried out on suspension of the compound, which suspension has been deagglomerated beforehand by treatment with ultrasound. The deagglomeration (or dispersion) under ultrasound is carried out using a Branson OSI sonifier (450 W) equipped with a probe with a diameter of 12 mm. The particle size measurement is carried out using a SediGraph particle sizer (sedimentation in the field of gravity+scanning with a beam of X-rays).
4 grams of compound (A) are weighed out in a sample tube (with a volume equal to 75 ml) and the weight is made up to 50 grams by addition of a 1 g/l sodium hexametaphosphate solution: an aqueous suspension comprising 8% of compound (A) is thus prepared, which suspension is homogenized for 2 minutes with magnetic stirring. Deagglomeration (dispersion) under ultrasound is then carried out as follows: after the probe has been immersed over a length of 4 cm, the output power is adjusted so as to obtain a deviation of the power needle indicating 20%. Deagglomeration is carried out for 180 seconds.
The particle size measurement is subsequently carried out by means of a SediGraph particle sizer. For this, the vertical rate of scanning of the cell by the beam of X-rays is first adjusted to 946, which corresponds to an analyzed maximum size of 63 xcexcm. Deionized water is circulated in said cell and then the electrical zero and the mechanical zero of the paper recorder are adjusted (this adjustment being carried out with the xe2x80x9c100%xe2x80x9d potentiometer of the recorder at the maximum sensitivity). The pen of the paper recorder is placed at the point representing the starting size of 85 xcexcm. The suspension of deagglomerated compound (A), optionally cooled beforehand, is subsequently circulated in the cell of the SediGraph particle sizer (the particle size analysis being carried out at 30xc2x0 C.) and the analysis then begins. The analysis is automatically halted as soon as the size of 0.3 xcexcm is reached (approximately 45 minutes). The level of fines (xcfx84f), that is to say the proportion (by weight) of particles with a size of less than 0.3 xcexcm, is then calculated.
This level of fines (xcfx84f) or level of particles with a size of less than 0.3 xcexcm increases in proportion as the compound increases in dispersibility.
In the second and third alternative forms in particular of the invention, the compound (A) employed exhibits a level of fines (xcfx84f) of at least 80%, in particular of at least 90%, indeed even of at least 95%.
In the second and third alternative forms of the invention, the starting amorphous aluminum hydroxycarbonate preferably comprises at least 0.01, in particular at least 0.04, mol of carbonate per mole of aluminum; it can comprise at least 0.1 mol of carbonate per mole of aluminum. In general, its carbonate/aluminum molar ratio is at most 0.25, in particular at most 0.2.
The carbonates present in this starting amorphous aluminum hydroxycarbonate and which can be detected by infrared spectroscopy are usually covalent.
This starting amorphous aluminum hydroxycarbonate generally has a BET specific surface area of between 40 and 150 m2/g, in particular between 45 and 95 m2/g; it can be between 50 and 75 m2/g.
It is generally formed of aggregates of individual particles which are not or not very porous, for example substantially spherical, with a size which can be between 15 and 25 nm.
It preferably has a low proportion of reactive surface Alxe2x80x94OH functional groups.
Likewise, the starting amorphous aluminum hydroxycarbonate preferably corresponds to the following emperical formula (I)
Al(OH)x(CO3)y.zH2Oxe2x80x83xe2x80x83(I)
in which
0.5xe2x89xa6xxe2x89xa63, for example 1xe2x89xa6xxe2x89xa63
0.01xe2x89xa6yxe2x89xa60.25, for example 0.04xe2x89xa6yxe2x89xa60.25, in particular 0.1xe2x89xa6yxe2x89xa60.25
zxe2x89xa61.5, for example zxe2x89xa61
In this formula (I), y can be at most equal to 0.2.
In the second and third alternative forms of the invention, the starting amorphous aluminum hydroxycarbonate, in particular when it corresponds to the empirical formula (I) mentioned above, can be prepared by the following process.
A precipitation reaction is carried out by introduction of a gas mixture, including carbon dioxide (CO2) gas, into a suspension of alkali metal aluminate, in particular of sodium aluminate, contained in a reaction chamber.
This sodium aluminate suspension can in particular exhibit a concentration, expressed in Al2O3, of between 10 and 150 g/l, in particular between 20 and 100 g/l; this concentration is, for example, between 40 and 70 g/l.
It generally has an Na2O/Al2O3 molar ratio of between 1 and 2, preferably between 1.15 and 1.75.
Its pH can vary, for example, between 11 and 13.5, in particular between 12 and 13.
The starting reaction temperature, that is to say the temperature of the aluminate suspension at the beginning of the introduction of the gas mixture, is usually set at at most 15xc2x0 C.; it is, for example, between 5 and 15xc2x0 C.
The reaction is generally carried out with stirring.
The gas mixture which is introduced into the reaction chamber preferably includes, in addition to the carbon dioxide gas, air. This gas mixture can then comprise 20 to 50%, in particular 30 to 40%, by volume of carbon dioxide gas and 50 to 80%, in particular 60 to 70%, by volume of air.
The pressure in the reaction chamber is maintained, throughout the reaction, preferably between 1.3 and 3.5 bar, for example between 1.7 and 2.5 bar.
The final reaction temperature should generally be at most 25xc2x0 C.; it is, for example, between 10 and 25xc2x0 C. It is preferable to maintain cooling in the reaction chamber during the carbonation.
The duration of the reaction (carbonation) can be between 10 and 60 minutes, for example between 10 and 30 minutes.
The pH of the reaction medium at the end of the reaction is generally between 9.5 and 10.5.
The control of the pH and of the temperature makes it possible to prevent the formation of an undesired phase, dawsonite.
The precipitate obtained is then usually filtered off and optionally washed, for example with water. Here, if any type of filtration means can be employed, use is advantageously made of a filter press.
The product obtained is then, optionally after resuspending (or reslurrying), dried, preferably by spraying, in particular using a sprayer of APV type, within a temperature for example of between 400 and 500xc2x0 C. and at a temperature for example of between 100 and 135xc2x0 C.
The amorphous aluminum hydroxycarbonate obtained can be subjected to a final milling operation by means of any suitable known device in order to xe2x80x9cbreak upxe2x80x9d the agglomerates/aggregates.
The rubber compositions in which the amorphous aluminum hydroxycarbonate or oxycarbonate is used as filler (in particular as reinforcing filler) are generally based on one or more elastomers.
Mention may more particularly be made, among suitable elastomers, of elastomers exhibiting a glass transition temperature of between xe2x88x92150 and +20xc2x0 C.
Mention may in particular be made, as possible elastomers, of diene elastomers.
For example, mention may be made of natural rubber, polymers or copolymers deriving from aliphatic or aromatic monomers comprising at least one unsaturation (such as, in particular, ethylene, propylene, butadiene, isoprene or styrene), poly(butyl acrylate), or their combinations; mention may also be made of silicone elastomers and halogenated elastomers.
The filler present in said rubber compositions is formed at least partially, in particular predominantly, by weight by the compound (A) composed of an amorphous aluminum hydroxycarbonate or hydroxyoxycarbonate or oxycarbonate. Another compound, such as precipitated silica, in particular a highly dispersible compound, can optionally be employed as filler but generally in a minor proportion by weight with respect to the compound (A).
These compositions preferably do not comprise precipitated silica as filler and/or the filler is formed entirely of the compound (A).
The rubber compositions generally comprise, in addition, at least one coupling agent and/or at least one coating agent.
The invention also relates to finished articles based on the rubber compositions described above. Mention may be made, as finished articles, of tire covers in particular the walls and the tread of tire, shoe soles, and the like.
The following examples illustrate the invention without, however, limiting the scope thereof.